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BRCA1 - the breast-ovary cancer (onco)gene - is the name of a gene located on chromosome 17 that is altered in certain families with an inherited susceptibility to breast cancer. It is a large, complex gene composed of 22 coding regions with over 100 deleterious mutations so far identified (> 300 have been predicted).
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(a) 10% (b) 50% (c) 75%. Women who inherit this altered gene have up to a 90% lifetime risk of developing breast cancer.
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> 50%. [Editors note: in developed countries, use of transvaginal ultrasonography (TVS) and/or CA125 levels to screen for ovarian cancer in families with the BRCA1 gene mutation is cost-effective. However, this is not yet the case in India.]
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Mutations in BRCA1 and BRCA2 genes are responsible for 5% of all breast cancers. Other common genes/gene mutations may account for up to 15% of cases:
- The Tp53 gene (may account for up to 1% of breast cancer cases diagnosed before the age of 35 years).
- The ATM gene (may account for 2 - 7% of breast cancers in the population).
- A mutation at the HRAS1 locus (thought to be associated with 3 - 8% of all breast cancers).
- A prophylactic oophorectomy substantially reduces a womans chances of dying from intraperitoneal carcinomatosis. Well described cases of peritoneal cancers indistinguishable from primary ovarian cancers have been described in women who have undergone prophylactic ovarian removal. Continued surveillance of such women is necessary.
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